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Showing papers on "Grain size published in 1983"


Journal ArticleDOI
TL;DR: In this article, the effect of the grain size on the ductility of the material was investigated and it was found that the ductile capacity of NiAl is independent of grain size for aggregates of grains larger than about 20 microns.

240 citations


Journal ArticleDOI
TL;DR: In this article, the formation of the second phases was linked to phase equilibria and grain growth that promoted compositional equilibration of the mullite phase, which suggested adjustments to phase boundaries in the high-temperature segment of the SiO2-Al2O3 phase diagram.
Abstract: Mullite ceramic, transparent in the infrared, was prepared by hot-pressing and hot-isostatically pressing starting materials derived from alkyloxides. A composition with 72.3 wt% Al2O3 yielded transparent, submicrometer grain size bodies at 1630°C, whereas higher temperatures produced glass-containing microstructures. A composition with 76 wt% A12O3 formed precipitates of α-Al2O3 at the consolidation temperature, which could be removed by subsequent annealing between 1800° and 1850°C. Spectral transmittance and absorption coefficients of the bodies are reported. The formation of the second phases was linked to phase equilibria and grain growth that promoted compositional equilibration of the mullite phase. The results suggest adjustments to phase boundaries in the high-temperature segment of the SiO2-Al2O3 phase diagram.

184 citations


Journal ArticleDOI
TL;DR: Rubie et al. as mentioned in this paper showed that reaction-enhanced ductility occurs when reaction boundaries are crossed during underthrusting rather than during the thermal readjustments of a perturbed geotherm following crustal thickening, or during uplift.

151 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of initial grain size on the transition from multiple to single peak flow was studied and the dependence of the stable dynamic grain size was determined, as were the density of twins and of deformation bands.
Abstract: Oxygen free high conductivity (OFHC) and electrolytic tough pitch (ETP) copper specimens of different grain sizes (10–800 μm) were tested at various constant true strain rates in a modified Instron testing machine. The temperature range investigated was 725–1075 K. The effect of initial grain size on the transition from multiple to single peak flow was studied. The dependence of the stable dynamic grain size on the temperature corrected strain rate and the steady state stress was determined, as were the density of twins and of deformation bands. The density of twins decreased as the initial grain size was increased and when the recrystallization mechanism changed from static to dynamic. The density of deformation bands increased markedly with initial grain size. As the deformation bands are preferential nucleation sites for new dynamic grains, the results indicate that the initial effective grain size D o *

145 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that nucleation can explain several important aspects of PSD behavior, such as the formation of fully developed domain walls by intervening energy barriers, and the creation and expansion of walls into the particle volume.
Abstract: The stable carriers of the paleomagnetic record in rocks are commonly fine pseudo-single-domain (PSD) particles between about 1 and 20 μm in diameter. However, the underlying mechanism which determines PSD behavior has previously remained in debate. To study this problem, magnetic domain patterns have been observed with the Bitter method on particles of natural pyrrhotite and intermediate titanomagnetite in various magnetization states, including natural remanent magnetization (NRM), after alternating field demagnetization of the NRM and during high-field hysteresis. From these observations it is evident that two primary mechanisms govern high-field hysteresis behavior: (1) ‘bulk’ pinning of fully developed domain walls by intervening energy barriers, and (2) nucleation, the creation and expansion of walls into the particle volume to produce a fully developed domain structure. These observations demonstrate that nucleation can explain several important aspects of PSD behavior. Typically, multidomain particles are entirely governed by bulk wall pinning, since they readily develop walls whose dimensions are comparable to the particle diameter prior to or upon removal of a strong field. For these grains the average domain wall spacing is relatively insensitive to the particular magnetization state, being approximately proportional to r (r being the grain diameter), in accordance with equilibrium calculations. In contrast, particles that are at least partially controlled by nucleation fail to develop a discernable domain wall structure at saturation remanence. However, these same grains can easily accommodate walls in other magnetization states. It is found that nucleation can involve two physically distinct but sometimes experimentally inseparable processes: (1) initial creation of walls at surface imperfections, and (2) unpinning of minute wall fragments from strong potential energy ‘traps’ near the grain surface. When either process fails, a grain remains locked in a metastable, single-domain-like state at saturation remanence and requires application of a reverse field Hn, called the nucleation field, before walls appear. In pyrrhotite, the probability for nucleation failure rises with decreasing grain size and has been determined through observation to be given by f(w = 0) = 1.2 exp (−0.46 r)r being in micrometers). Such single-domain-like particles can thus contribute substantially to the saturation remanence in the PSD range. The nucleation field determined experimentally for pyrrhotite is given by Hn ≃ 1200/ r Oe. In many fine pyrrhotites, Hn is sufficiently strong to reverse completely the magnetization through a single Barkhausen jump of the nucleated wall. These observations thereby demonstrate that nucleation becomes increasingly more dominant as the particles become smaller, a manifestation of the random distribution of active nucleation sites. Nucleation may therefore account for much of the magnitude and grain size dependence of hysteresis parameters in the PSD range as well as resulting in a gradual transition between multidomain and PSD behavior. Fine particles completely controlled by nucleation during hysteresis behave in a strikingly parallel manner to classical single domains and are therefore quite appropriately described as being pseudo-single-domain.

128 citations


Journal ArticleDOI
01 Nov 1983-Icarus
TL;DR: In this paper, the authors investigated the effect of grain size on the strength of absorption features observed in the reflectance of a particulate surface on a planetary surface containing volatile ices and found that the absorption characteristics can change in connection with processes leading to a change in the grain size of the material.

117 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the compositions of the films using Auger electron spectroscopy and their structure and morphology studied using X-ray diffraction and scanning electron microscopy respectively.

116 citations


Journal ArticleDOI
TL;DR: In this paper, a large collection of mostly continental igneous rocks are reported, whose magnetic carriers were believed from previous work to be of one of three types: MD (multidomain), SD/PSD (single domain/pseudo-single-domain), or a bimodal mixture of MD grains (e.g., discrete opaques) and SD/PsD material (e., silicate inclusions).

98 citations


01 May 1983
TL;DR: In this article, an analysis of ice fracture that incorporates dislocation mechanics and linear elastic fracture mechanics is discussed, and derived relationships predict a brittle to ductile transition in polycrystalline ice under tension with a Hall-Petch type dependence of brittle fracture strength on grain size.
Abstract: : An analysis of ice fracture that incorporates dislocation mechanics and linear elastic fracture mechanics is discussed. The derived relationships predict a brittle to ductile transition in polycrystalline ice under tension with a Hall-Petch type dependence of brittle fracture strength on grain size. A uniaxial tensile testing technique, including specimen preparation and loading system design was developed and employed to verify the model. The tensile strength of ice in purely brittle fracture was found to vary with the square root of the reciprocal of grain size, supporting the relationship that the theory suggests. The inherent strength of the ice lattice and the Hall-Petch slope are evaluated and findings discussed in relation to previous results. Monitoring of acoustic emissions was incorporated in the tests, providing insights into the process of microfracture during ice deformation.

89 citations


Journal ArticleDOI
TL;DR: Olivine and spinel in peridotites from the Miyamori ultramafic complex and the Ichinogemata crater of Northeast Japan show a systematic variation in the Mg/ (Mg+Fe) ratio which is correlated mainly with the grain size of spinel as discussed by the authors.
Abstract: Olivine and spinel in peridotites from the Miyamori ultramafic complex and the Ichinogemata crater of Northeast Japan show a systematic variation in the Mg/ (Mg+Fe) ratio which is correlated mainly with the grain size of spinel. This correlation can be explained by a diffusion model assuming a semi-infinite composite sphere under cooling or heating conditions. In order to obtain absolute temperatures of thermal events, the olivine-spinel geothermometer is applied to pairs of spinel core and olivine core (average composition). The calculated temperatures range over two hundred degrees and have a systematic relationship with the grain size of spinel. In the Miyamori complex, the calculated temperatures decrease monotonically with decrease in grain size of spinel, whereas in the Ichinomegata lherzolite nodule those of spinel smaller than 0.2 mm increase as the grain size decreases and those of spinel larger than 0.2 mm remain constant regardless of further increase in grain size. These observations, in the light of the diffusion model, suggest that the Miyamori complex may have cooled from higher than 800° C to lower than 600° C and that the lherzolite nodule from the Ichinomegata crater may have been in equilibrium at 900° C before it was heated above 1,100° C for less than a few days. These two examples indicate that olivine-spinel pairs of peridotites do not always indicate an appropriate equilibration temperature. We cannot interpret the supposed equilibration temperatures until the existence of isothermal stages in the thermal history of peridotites is established by carefully checking the chemical heterogeneity.

89 citations


Journal ArticleDOI
TL;DR: In this article, the volume fraction of twinned material has been measured at the surface and in the bulk and it is shown that this volume fraction is a linear function of both strain and grain size in most cases.
Abstract: The incidence of deformation twinning in samples of a commercial rolled zinc-0.1% aluminium-0.05 wt % magnesium alloy has been measured at room temperature as a function of strain, grain size and direction of loading relative to the rolling direction. The volume fraction of twinned material has been measured at the surface and in the bulk. It is shown that this volume fraction is a linear function of both strain and grain size in most cases. Bands of heavily twinned grains are found to form inhomogeneously across the gauge length of tensile specimens, by an autocatalytic mechanism. Several examples are given of the interaction of twins and slip bands at grain boundaries which illustrate the formation and the accommodation of twins. The smaller volume fraction of twins found at the surface compared with the bulk reflects a relaxation of Von Mises criterion.

Journal ArticleDOI
TL;DR: In this paper, the ductile Ll2-type y′ wires with circular cross section have been found in rapidly quenched Ni-Al-X (X = Cr, Mn, Fe, Co, or Si) ternary systems.
Abstract: Ductile Ll2-type y′ compounds with rather high strengths and large elongations have been found in rapidly quenched Ni-Al-X (X = Cr, Mn, Fe, Co, or Si) ternary systems. The y′ compounds consist of a metastable phase which contains numerous APD with a size as small as about 50 to 75 nm. Further, the ductile y′ wires with circular cross section have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter is in the range of 85 to 190 µm and the average grain size is about 2 to 5 µam. The Hv, σy, σf, and eρ of the y′ wires are about 240 to 400 DPN, 390 to 590 MPa, 580 to 910 MPa, and 4 to 10 pct, respectively, for Ni-Al- (Cr, Fe, Co, or Si) systems and about 220 DPN, 260 MPa, 440 MPa, and 27 pct, respectively, for the Ni-Al-Mn system. A cold drawing causes a significant increase in σy and σf and the attained values are about 2450 MPa and 2480 MPa, respectively, for Ni-20Al-10Cr wire drawn to about 90 pct reduction in area. Around the temperatures where the APB disappear on annealing, the Hv, σy, σf, and egr of the y′ wires decrease significantly accompanied with a drastic change in fracture surface morphology from a transgranular type to an intergranular type. It has been therefore inferred that the high strengths and good ductility of the melt-quenched y′ compounds are due to the structural changes to a low degree of ordered state containing a high density of APB and the suppression of grain boundary segregation.

Journal ArticleDOI
TL;DR: In this paper, the relationship between average grain size on the surface of SnO 2 transparent conductive film and conversion efficiency of the a-Si:H solar cell was investigated.
Abstract: The relationship between average grain size on the surface of SnO 2 transparent conductive film and conversion efficiency of the a-Si:H solar cell was investigated. a-Si:H solar cells were fabricated on SnO 2 /glass substrates with various grain sizes. The cell structure was glass/p(SiC)-i-n/Al and the effective cell area was 4 × 10-2cm2. The reflectivity from the glass substrate was reduced to about 7 percent with increasing the grain size from 0.1 to 0.8µm, and the short-circuit current was inceased from 12 to 14mA/cm2. A 7.9 percent of conversion efficiency was achieved using milky SnO 2 film of 0.4-µm average grain size at AM-100mW/cm2.

Journal ArticleDOI
TL;DR: In this article, the authors describe aspects of the microstructural evolution and associated small-scale motion in a dynamically recrystallizing sheet of octachloropropane, and reveal an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient.
Abstract: Advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes, and the effects of these processes upon various fabric elements. This paper describes aspects of the microstructural evolution and associated small-scale motion in a dynamically recrystallizing sheet of octachloropropane. The material was deformed in progressive pure shear, at 2×10−3 sec−1 (with interruptions for photography and U-stage measurement), at 70 % of its absolute melting temperature. The dominant recrystallization process is migration of grain boundaries, with consequent major adjustment of the shapes and sizes of grains, but no marked change in the average grain size and no creation of new grains. Typical grains in the fully deformed material (30% bulk shortening) have a composite structure with primitive, high-strain regions inherited directly from the undeformed state, rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries. An array of second-phase marker particles permits distinction between grain boundary motion with and through the material, and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient. The markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains. The central problem posed by the observations is to explain the direction and speed of each migrating boundary. Two hypotheses were tested, neither with outstanding success. One of these hypotheses is that grain boundary migration is part of a strain accomodation process, that operates between grains stretching or shortening at different rates parallel to their mutual boundary.

Journal ArticleDOI
TL;DR: In this article, a weak link statistical model was proposed to predict the critical fracture distance from the crack tip at which the probability of cleavage cracking exhibits a maximum, which depends on the size distribution and volume fraction of carbides.
Abstract: The fracture of mild steel in the cleavage range has been evaluated using a weakest link statistical model, assuming the preexistence of a distribution of cracked carbides. The model provides a rationale for the critical fracture distance, viz., the distance from the crack tip at which the probability of cleavage cracking exhibits a maximum. The critical distance depends on the size distribution and volume fraction of carbides. The model also predicts trends in K,ic with material properties: flow strength, cracked carbide size and volume fraction, and grain size. The resultant temperature dependence of K,ic is shown to derive exclusively from the temperature dependence of the flow stress, as in prior models. The effects of microstructure on K,ic depend primarily on the size distribution of cracked carbides, with additional influences of the grain size and of the volume fraction of carbides.

Journal ArticleDOI
Minyoung Lee1
TL;DR: In this paper, the effect of crystallographic orientation and test temperature on hardness of WC single crystals was investigated along with the hot hardness of poly crystalline tungsten carbide.
Abstract: The effect of crystallographic orientation and test temperature on hardness of WC single crystals was investigated along with the hot hardness of poly crystalline tungsten carbide. Also investigated was the effect of carbide grain size and the amount of binder phase on the hot hardness of some cemented tungsten carbides. The hot hardness of single crystal WC on all major crystallographic orientations evaluated decreases very rapidly for increasing temperature, and the single crystal hardness on its hardest orientation is only about half of the polycrystalline material depending on the test temperature. Because of its polycrystalline character, some cobalt bonded cemented tungsten carbides can be harder than single crystal WC over some intermediate temperature range.

Journal ArticleDOI
TL;DR: In this paper, reactively sputtered ZrN, the most thermally stable of the refractory metal nitrides, for its diffusion barrier properties in aluminum metallization schemes with Rutherford backscattering spectroscopy and transmission electron microscopy (TEM).

Journal ArticleDOI
TL;DR: In this article, the influence of alloy grain size on growth rates of surface cracks 20 to 500 μm in length was studied in Al 7075-T6 specimens prepared in 12 and 130 μn grain sizes.
Abstract: The influence of alloy grain size on growth rates of surface cracks 20 to 500 μm in length was studied in Al 7075-T6 specimens prepared in 12 and 130 μn grain sizes. Grain boundaries temporarily interrupt the propagation of cracks shorter than several grain diameters in length. Linear elastic fracture mechanics is inadequate to describe resulting average growth rates which must instead be characterized as a function of cyclic stress amplitude, σa, and alloy grain size as well as stress intensity range, σK. These observations are rationalized using two models, one that relates crack closure stress to alloy grain size, and a second that relates the development of microplasticity in a new grain in the crack path to grain size. In addition, growth rates were found to be faster in fully reversed loading than in tension-tension loading, especially in the large grained material. Evidence is presented to demonstrate that this is a consequence of the fatigue induced development of a compressive residual surface stress during tension-tension loading. These complex effects, and the role of grain size in determining short crack growth, are discussed.

Journal ArticleDOI
TL;DR: In this paper, the relationship between porosity and formation factor has been found to have a general form K = r · F−s, where s is constant and r is a function of the mean size d of the small component of the samples.
Abstract: Laboratory investigations have been carried out on one- and two-component artificial sand samples in order to estimate the relations between formation factor (F), porosity (φ), and permeability (K). The measurements were carried out by varying grain size and size distribution while keeping constant shape and packing; in our experimental conditions the measured formation factor approximated the intrinsic formation factor. The relationship between formation factor and porosity (F = a ·φ−m) is independent of grain size and size distribution; the coefficient values are: a = 1·15, m = 1·42. The relationship between permeability and formation factor has the general form K = r · F−s, where s is constant, and r is a function of the mean size d of the small component of the samples. The K-F relation can be established only if d is constant; in these conditions the relationship is an inverse one, and the negative trend is related to the variations in size distribution.

Journal ArticleDOI
TL;DR: In this paper, a model for the growth of cracks by cavitation has been developed in which the effect of a viscous constraint has been considered, and the velocity of the crack is predicted by this model to be proportional to K and inversely proportional to q. The influence of the constraint was shown to be important only for small damage zones, and high values of both the relative cavity spacing (f/l) and the cavity area at coalescence.

Journal ArticleDOI
TL;DR: In this article, a linear relation with the inverse square root of the average grain size is found for stabilised ZrO2-Y2O3 ceramics with varying grain sizes and microstructures with the help of different preparation techniques.
Abstract: Stabilized ZrO2-Y2O3 ceramics have been prepared with varying grain sizes and microstructures with the help of different preparation techniques. Bi2O3 has been added as a sinter aid to some of the samples. This results in a certain amount of a zirconia-rich second phase. For Bi2O3-free samples the fracture toughness (K lc), and therefore the fracture energy, increases with decreasing grain size. A linear relation with the inverse square root of the average grain size is found. The highest value ofK lc amounts to 4.1 MPa m1/2. Fracture toughness values of 1.9±0.2 MPa m1/2 are measured for Bi2O3 containing materials. The fracture surfaces are intergrannular for Bi2O3-containing and transgranular for Bi2O3-free samples, respectively.

Journal ArticleDOI
TL;DR: In this article, the tensile flow stress for superpure and commercial aluminium and for an Al-21/4% Mg alloy in relation to strain, grain size d, subgrain or cell size and dislocation density ρ was studied.
Abstract: The tensile flow stressσ∊ has been studied for super-pure and commercial aluminium and for an Al-21/4% Mg alloy in relation to strain, grain size d, subgrain or cell size and dislocation density ρ. At room temperature and 200°C, the flow stress depends on both ρ1/2 and d −1/2. This is interpreted an evidedce of a requirement inσe that slip can be transmitted across a grain boundary. There is extensive dislocation annihilation during deformation at these two temperatures, particularly in the two aluminiums and particularly in fine grains. The behaviour of the commercial aluminium is unusual. At room temperature, the retained ρ is higher in coarse than in fine grains. However, the flow stress remains higher in the fine grains because of the slip transmission requirement. At 200°C, the dislocation density is so much higher in the coarse grains that the flow stress is also higher. At 400°C, most of the dislocations are annihilated and sharp subgrains form with planar network boundaries. It is propose...

Journal ArticleDOI
TL;DR: In this article, the effect of sample and grain size on the uni- axial compressive strength of polycrystalline ice has been investigated at -10·C, at a strain-rate of 5.5 x 10-4 S-1.
Abstract: The effect of sample and grain size on the uni­ axial compressive strength of polycrystalline ice has been investigated at -10·C, at a strain-rate of 5.5 x 10- 4 S-1. The results show (a) that the sample size must be 12 or more times greater than the grain size for it to have no effect on the strength and (b) that there is no significant dependence of compressive strength on grain size, within the grain­ size range of 0.6 to 2.0 mm.

Journal ArticleDOI
TL;DR: In this article, two tungsten powders have been treated with small concentrations of sintering activators to provide for enhanced low-temperature Sintering, and the experimental study focused on the determination of the processing effects on properties such as sintered density, grain size, hardness, and strength.
Abstract: Two tungsten powders have been treated with small concentrations of sintering activators to provide for enhanced low temperature sintering. The experimental study focused on the determination of the processing effects on properties such as sintered density, grain size, hardness, and strength. Variables in the plan included tungsten particle size, type of activator, amount of activator, compaction pressure, and sintering temperature. The sintered density is found to have a dominant effect on strength and hardness. The various processing variables are analyzed in terms of their effects on density. At high sintered densities, grain growth acts to degrade the strength. Additionally, the nature of the sintering activator influences the fracture strength. In this study optimal strength occurred with a 0.7 μm tungsten powder treated with 0.29 wt pct Ni, sintered at 1200 °C for one hour. The resulting density was 18.21 g/cm3, with aR A hardness of 69 and a transverse rupture strength of 460 MPa.

Journal ArticleDOI
TL;DR: In this article, a commercial Airco wire containing 2869 Nb filaments of 3-5 μm diameter in a matrix with a bronze/Nb ratio of three was given a variety of reaction heat treatments and analyzed as a function of heat treatment, and found to be divisible into three concentric shells that are morphologically distinct.
Abstract: The superconducting phase within a bronze‐process, multifilamentary Nb3Sn superconducting wire is formed by reaction at the interface between the Nb filaments and the bronze matrix. The maximum current that can be carried by the wire is known to depend on the time and temperature of the heat treatment as well as on the transverse magnetic field. In the work reported here a commercial Airco wire containing 2869 Nb filaments of 3–5 μm diameter in a matrix with a bronze/Nb ratio of three was given a variety of reaction heat treatments. The microstructure of the reacted layer was analyzed as a function of heat treatment, and found to be divisible into three concentric shells that are morphologically distinct. The central shell consists of fine equiaxed grains. Its areal fraction, grain size, and composition depend on the heat treatment, and appear to determine the critical current. The best combination of grain size and composition, and the highest critical current, is obtained with an intermediate reaction temperature (700–730 °C). A further improvement in both microstructure and critical current is achieved by double‐aging the wire, starting the reaction at 700 °C and finishing it at 730 °C. The relation between microstructure and heat treatment is interpreted in light of the apparent mechanism of the reaction, which is revealed by high resolution analyses of the reacted layer. The relation between microstructure and properties is consistent with current understanding of the influence of grain size and stoichiometry on the behavior of type II superconductors.

Journal ArticleDOI
TL;DR: In this paper, the microstructural changes which occur during the extrusion of an Al-7Mg alloy have been investigated using optical and electron microscopy, and it was concluded that the high solute content hinders dislocation motion, and nucleation of dynamic recrystallization occurs at dislocation clusters and/or at small parti...
Abstract: The microstructural changes which occur during the extrusion of an Al–7Mg alloy have been investigated using optical and electron microscopy. Light microscopy has shown that recrystallized grains are present both at the original grain boundaries and within the grains, even at the breakthrough pressure. Electron microscopy has shown that a large percentage of recrystallized grains contain a substructure and are thus dynamically recrystallized. The grain size of these dynamically recrystallized grains is usually less than 5 μm. Some hot rolling, and cold rolling followed by annealing, experiments have also been performed to substantiate the evidence for dynamic recrystallization. A large number of recrystallized grains were observed, although the bulk of the material deformed with dynamic recovery as the operative mechanism. It is finally concluded that the high solute content hinders dislocation motion, and nucleation of dynamic recrystallization occurs at dislocation clusters and/or at small parti...

Journal ArticleDOI
TL;DR: In this paper, a method for making lowvoltage ZnO varistors having extraordinarily large grain size without necessity of sintering at much higher temperatures or for much longer times is reported.
Abstract: A method for making low‐voltage ZnO varistors having extraordinarily large grain size without necessity of sintering at much higher temperatures or for much longer times is reported. The device is made by sintering a mixture of ZnO fine powder, additives, and ZnO seed grains having grain sizes of 63–105 μm obtained by washing a ZnO sintered body containing BaO in boiling water. The device has a grain size around 500 μm and low threshold voltage of 6 V/mm. Such anomalous grain growth is caused by the difference between the radii of curvature of ZnO fine powder and ZnO seed grains.

Journal ArticleDOI
TL;DR: In this paper, a 2D investigation of the band curvature near a grain boundary has been carried out on transistors made in laser recrystallized polycrystalline silicon.
Abstract: Measurements have been carried out on transistors made in laser recrystallized polycrystalline silicon. In these devices, grain size is comparable to channel dimensions. A 2-D investigation of the band curvature near a grain boundary has made it possible to model transistor characteristics. Good agreement has been found between theory and experiments.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the minority carrier mobility depends on the grain size even when this size is larger than 0.1 mm, which explains that generally the electronic properties are degraded at the bottom or at the periphery of the ingots where the dislocation density is high and at the top where the impurities are concentraled by the Bridgman process.
Abstract: Lifetimes (τn), diffusion lengths (Ln) and consequently mobilities (μn) of minority carriers and also mobilities (μp) of majority carriers have been measured on small MESA diodes (1.5 × 1.5 mm) revealed on photocells realized on boron-doped cast polysilicon obtained by a fast variant Bridgmen method. The lifetime τn and the diffusion length Ln decrease drastically when the number of grains per diode NG increases. It has been deduced that the minority carrier mobility μn depends on the grain size even when this size is larger than 0.1 mm. This influence of the grain size is often screened by intragrain defects. This explains that generally the electronic properties are degraded at the bottom or at the periphery of the ingots where the dislocation density is high and at the top where the impurities are concentraled by the Bridgman process.

Journal ArticleDOI
TL;DR: In this article, the relative importance of shape-selectivity due to channel size limitations and zeolitic grain size in the conversion of methanol to higher hydrocarbons on Pentasil-type zeolites, several catalysts were prepared using different synthesis and acidification procedures.